1. Field of the Invention
This invention relates to implantable medical devices such as stents. More particularly, this invention relates to modifications made to the surface of the device for providing a platform for attachment of biocompatible materials or a coating, such as a polymeric coating used for the delivery of a therapeutic substance.
2. Description of the Background
Stents act as scaffoldings, functioning to physically hold open and, if desired, to expand the wall of the passageway. Typically stents are capable of being compressed, so that they can be inserted through small cavities via catheters, and then expanded to a larger diameter once they are at the desired location. Mechanical intervention via stents has reduced the rate of restenosis; restenosis, however, is still a significant clinical problem. Accordingly, stents have been modified to function not only as mechanical scaffolding, but also to provide biological therapy.
Biological therapy can be achieved by medicating the stents. Medicated stents provide for the local administration of a therapeutic substance at the diseased site. In order to provide an efficacious concentration to the treated site, systemic administration of such medication often produces adverse or toxic side effects for the patient. Local delivery is a preferred method of treatment in that smaller total levels of medication are administered in comparison to systemic dosages, but are concentrated at a specific site. Local delivery thus produces fewer side effects and achieves more favorable results.
A common method of medicating a stent is by depositing a polymeric coating, impregnated with a therapeutic substance, on the surface of the stent. A polymer dissolved in a solvent is applied to the stent. A therapeutic substance can be dissolved or dispersed in the composition. The solvent is allowed to evaporate to form the coating. The application of the composition can be performed by spraying the composition on the stent or immersing the stent in the composition.
Various factors can lead to delamination of the polymeric coating from the surface of the stent. One example of such a factor includes mechanical stress caused by the radial expansion of the stent body. Additionally, polymeric materials have a tendency to adhere poorly to metallic materials, such as stainless steel, from which a stent is made. The embodiments of the present invention address such deficiencies by providing a modified stent surface and methods of forming a coating on the stent surface.